Ultrastructural Changes in Gill Epithelia of a Yellowtail, Seriola quinqueradiata, Exposed to Sea Bloom

Abstract

Surface structures of the gill epithelia of a yellowtail, S. quinqueradiata, were observed with a scanning electron microscope after exposure to sea bloom. The fish was on the verge of death 45 min after exposure in a circuit tank containing a quantity of plankton, including Gymnodinium. Morphological changes in the gill epithelia of the primary and secondary lamellae were observed on the afferent side. Pavement cells of the afferent side were swollen remarkably, but cells on the efferent side were intact. Chloride and mucous cells with many cellular extensions appeared in the epithelia of the afferent edge of the primary lamellae. Chloride cells were found on the interlamellar space of the secondary lamellae as well. These chloride and mucous cells could not be seen clearly on gill filaments exposed to normal sea water. The significance of morphological changes due to lower salinity and their relation to the toxic effects of plankton were discussed.